Apparatus for shaping thermoplastic sheets

ABSTRACT

APPARATUS FOR CHAPING PLASTIC SHEETS USED AS INTERLAYERS IN LAMINATED SAFETY GLASS. THE APPARATUS COMPRISES AN ELONGATED HEATING OVEN AND AN ELONGATED COOLING TUNNEL POSITIONED ABOVE THE HEATING OVEN AND HAVING ITS ENTRANCE END DISPOSED OPPOSITE THE EXIT END OF SAID HEATING OVEN. THE PLASTIC SHEETS ARE CARRIED IN A VERTICAL POSITION BY SUPPORTING FRAMES WHICH ARE CONVEYED SUCCESSIVELY THROUGH THE HEATING OVEN AND COOLING TUNNEL. MEANS IS PROVIDED FOR INTRODUCING HEATED AIR INTO THE HEATING OVEN AND FOR CIRCULATING IT AROUND AND BETWEEN THE PLASTIC SHEETS TO CAUSE THEM TO SAG IN THE PLANE OF THE SHEETS TO EFFECT THE SHAPING THEREOF, WHILE MEANS IS PROVIDED FOR INTRODUCING CONDITIONED AIR INTO THE COOLING TUNNEL ADJACENT THE EXIT END THEREOF AT A PRESSURE SUFFICIENT TO CAUSE IT TO FLOW TOWARD THE ENTRANCE END THEREOF AROUND AND BETWEEN THE PLASTIC SHEETS MOVING IN THE OPPOSITE DIRECTION TO COOL AND CONTROL THE MOISTURE CONTENT OF SAID SHEETS.

Jan. 12, 1971 A, H M|| LR ETAL 3,553,771

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APPARATUS FOR SHAPING THERMOPLASTIC SHEETS Filed April 2, 1968 .1,9 Sheets-Share?I l 7 4- IVENToRs mll. vm A, H, MULLER ETAL APPARATUS FOR SHAPING THERMOPLASTIC SHEETS Filed April 2, 1968 19 Sheets-Sheet 18 lm. E2, 19H A.H.M|LLER ETAL Egm `APPAR'IUS FOR SHAPING THERMOPLASTIC SHEETS Filed April n. 196s 19 sheets-sheet 19 United States PatentY Office U.s. Cl. 1s-19 7 claims ABSTRACT F THE DISCLOSURE Apparatus for chaping plastic sheets used as interlayers in laminated safety glass. Theapparatus comprises an Patented Jan. 12, 19.71

tion first through a heating zone and then through a cooling zone. During the heating of the sheets, tractive forces applied to the lower unsupported edges thereof will cause said sheets to be distorted inthe plane of the sheets to the desired curvature or shape. In certain cases, however, depending'upon the size of the plastic sheets and the degree of shaping required, the use of tractive `forces is not neceselongated heating oven and an elongated cooling tunnel positioned above the heating oven and having its entrance end disposed oppositethe exit end of said` heating oven. The plastic sheets are carried in a vertical position by supporting frames which are conveyed successively through the heating oven and cooling tunnel. Means is provided for introducing heated air into the heating oven and-for circulating it around and between the plastic sheets to cause them to sag in the plane of the sheets to effect the shaping thereof, while means is provided for introducing conditioned air into the cooling tunnel adjacent the exit end thereof at a pressure sufficient to cause it to flow t'oward the entrance end thereof around and between the plastic sheets moving in the opposite direction to cool and control the moisture content of said sheets. l

This applicationY is a continuation-in-part of application Ser. No. 705,234, tiled July 18, 1967, which is in turn a division of application Ser. No. 405,383, led Oct.' 2l, 1964, now Pat. No. 3,341,889.

The present invention relates generally to the manufacture of glare-reducing windows, or the like and more particularly to an improved apparatus forl shaping the plastic interplayer for curved or bent laminated safety glass windsary to induce shaping.

As herein provided, the air in both the heating zone and cooling zone is maintained within desired ranges of workingtemperatures whereby the plastic sheets will become shapedwhile heat-softened and then set in the desired curvature to which they were `shaped as they are cooled. To obtain gradual drying of the sheets as they cool, conditioned air is supplied to the cooling zone and as the frames reach the exit end of said cooling zone, they are successively conveyed with the shaped sheets into a room of closely controlled temperature and humidity to obviate the tendency of the plastic to re-laX, due to its elastic memory, from the curvature to which it was shaped. The plastic sheets are maintained under such controlled conditions until assembled with the glass sheets in the manufacture of laminated safety glass.

It is therefore a primary object of the present invention to provide an improved apparatus for shaping sheets of plastic material employed as the interlayer in the producshields or windows when said interl-ayer is provided with a glare-reducing portion. Inshaping the plastic interlayers for laminated safety glass windshields or windows, it has been customary to rst cut a continuous length or roll of plastic into individual sheets, and then clamp eachindividual sheet along two opposite edges only in a frame to hold it in its. normal shape. Tractive forces are then applied to the lower unt supported edge of the sheetwhile supporting the frame and sheet in a vertical position and simultaneously heating the sheet until it has been shaped in the desired manner. After heating, the sheet is cooled to retain its desired shape. It has heretofore been thel practice to clamp only a single sheet of plastic in a frame, `with a plurality of such frames being hung in a vertical position on a rack or truck which is then passed rst into a heating chamber and subsequently into a cooling chamber. t

While the invention is applicable to the shaping of individual plastic sheets supported in separate frames, it is of particular utility where a plurality of continuous lengths of thermoplastic material are withdrawn from separate sources of supply and, while superimposed one upon the other, are clamped at their free ends in a frame and uniformly placed in tension. While maintained in tension, the continuous lengths of plastic are also clamped in the frame at a point remote from the free `ends thereof and then cut transversely from the continuous lengths outwardly of the frame to provide a plurality of individual sheets. A succession of frames, each with a plurality of uniformly taut or tensioned sheets clamped therein, are supported in vertical position and moved in spaced relation of curved or bent laminated safety glass windows or windshields having a glare-reducing area in a substantially continuous manner.

Another object of the invention is to provide apparatus for shaping plastic sheets having a colored band along and parallel to one marginal edge of the sheet, in which a substantially continuous length of plastic material is withdrawn from a source of supply and clamped at the free end thereof in one end of a frame and also clamped at a point remote from said free end in the opposite end of said frame, the plastic being then cut transversely outwardly of the frame to form an individual sheet of predetermined size, the frame with the sheet clamped therein being hung in a vertical position with the colored band at the upper edge thereof, the sheet then heated and caused to be deflected downwardly in the plane of said sheet resulting in the upper and lower longitudinal edges thereof being curved in the same direction, after which the sheet is cooled.

Another object of the invention is `to provide such an apparatus in which a plurality of substantially continuous lengths of plastic material are drawn from a plurality of` sources of supply and sections of predetermined length transversely clamped in a0 frame along two spaced lines in such a manner as to place the clamped sections under uniform tension, after which the continuous lengths of plastic are cut transversely outwardly of the frame to provide indivi-dual sheets which are shaped in the above mannen `Another object of the invention. is to provide such an apparatus in which the substantially continuous lengths of plastic material are drawn from the sources of supply in superimposed contacting relation between a pair of feed rolls and the free ends thereof clamped together, after which the feed rolls are moved outwardly to place the plastic material under tension, the plastic material being then clamped inwardly of the free ends thereof to provide uniformly taut sections of predetermined length before the continuous lengths of plastic are cut to :form individual sheets.

A further object of the invention is to provide such an apparatus in which the plurality of substantially continuous lengths of plastic material after being drawn from their separate sources of supply and before passing between the feed rolls are permitted, while hanging in freely suspended loops, to relax and obtain a uniformity of lineal 

